FIRST-PRINCIPLES MOLECULAR-DYNAMICS STUDY OF CO ADSORPTION ON THE SI(001) SURFACE

We present first-principles molecular dynamics calculations of CO adso rption on the Si(001) surface. We found two adsorption sites of CO on the Si(001) surface, on which the CO molecule adsorbs symmetrically an d asymmetrically. The asymmetric structure is preferable: the calculat ed adsorption energies are 17.0 and 19.0 kcal/mol, respectively, on th e symmetric and asymmetric sites. The electron density analysis shows that the main interaction between CO and the Si(001) surface is sigma- donation on the asymmetric sites and pi-back-donation on the symmetric sites. The calculated vibrational frequency of the CO stretch for the asymmetric site agrees well with the experimental HREELS spectra. The symmetric structure may also exist considering the small difference i n the adsorption energy. (C) 1998 Elsevier Science B.V. All rights res erved.